| 1 |
<?php |
| 2 |
/* |
| 3 |
* Copyright 2008 Google Inc. |
| 4 |
* |
| 5 |
* Licensed under the Apache License, Version 2.0 (the "License"); |
| 6 |
* you may not use this file except in compliance with the License. |
| 7 |
* You may obtain a copy of the License at |
| 8 |
* |
| 9 |
* http://www.apache.org/licenses/LICENSE-2.0 |
| 10 |
* |
| 11 |
* Unless required by applicable law or agreed to in writing, software |
| 12 |
* distributed under the License is distributed on an "AS IS" BASIS, |
| 13 |
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 14 |
* See the License for the specific language governing permissions and |
| 15 |
* limitations under the License. |
| 16 |
*/ |
| 17 |
|
| 18 |
/* |
| 19 |
* This class implements a basic on disk storage. While that does |
| 20 |
* work quite well it's not the most elegant and scalable solution. |
| 21 |
* It will also get you into a heap of trouble when you try to run |
| 22 |
* this in a clustered environment. In those cases please use the |
| 23 |
* MySql back-end |
| 24 |
* |
| 25 |
* @author Chris Chabot <chabotc@google.com> |
| 26 |
*/ |
| 27 |
class apiFileCache extends apiCache { |
| 28 |
private $path; |
| 29 |
|
| 30 |
public function __construct() { |
| 31 |
global $apiConfig; |
| 32 |
$this->path = $apiConfig['ioFileCache_directory']; |
| 33 |
} |
| 34 |
|
| 35 |
private function isLocked($storageFile) { |
| 36 |
// our lock file convention is simple: /the/file/path.lock |
| 37 |
return file_exists($storageFile . '.lock'); |
| 38 |
} |
| 39 |
|
| 40 |
private function createLock($storageFile) { |
| 41 |
$storageDir = dirname($storageFile); |
| 42 |
if (! is_dir($storageDir)) { |
| 43 |
if (! @mkdir($storageDir, 0755, true)) { |
| 44 |
// make sure the failure isn't because of a concurrency issue |
| 45 |
if (! is_dir($storageDir)) { |
| 46 |
throw new apiCacheException("Could not create storage directory: $storageDir"); |
| 47 |
} |
| 48 |
} |
| 49 |
} |
| 50 |
@touch($storageFile . '.lock'); |
| 51 |
} |
| 52 |
|
| 53 |
private function removeLock($storageFile) { |
| 54 |
// suppress all warnings, if some other process removed it that's ok too |
| 55 |
@unlink($storageFile . '.lock'); |
| 56 |
} |
| 57 |
|
| 58 |
private function waitForLock($storageFile) { |
| 59 |
// 20 x 250 = 5 seconds |
| 60 |
$tries = 20; |
| 61 |
$cnt = 0; |
| 62 |
do { |
| 63 |
// make sure PHP picks up on file changes. This is an expensive action but really can't be avoided |
| 64 |
clearstatcache(); |
| 65 |
// 250 ms is a long time to sleep, but it does stop the server from burning all resources on polling locks.. |
| 66 |
usleep(250); |
| 67 |
$cnt ++; |
| 68 |
} while ($cnt <= $tries && $this->isLocked($storageFile)); |
| 69 |
if ($this->isLocked($storageFile)) { |
| 70 |
// 5 seconds passed, assume the owning process died off and remove it |
| 71 |
$this->removeLock($storageFile); |
| 72 |
} |
| 73 |
} |
| 74 |
|
| 75 |
private function getCacheDir($hash) { |
| 76 |
// use the first 2 characters of the hash as a directory prefix |
| 77 |
// this should prevent slowdowns due to huge directory listings |
| 78 |
// and thus give some basic amount of scalability |
| 79 |
return $this->path . '/' . substr($hash, 0, 2); |
| 80 |
} |
| 81 |
|
| 82 |
private function getCacheFile($hash) { |
| 83 |
return $this->getCacheDir($hash) . '/' . $hash; |
| 84 |
} |
| 85 |
|
| 86 |
public function get($key, $expiration = false) { |
| 87 |
$storageFile = $this->getCacheFile(md5($key)); |
| 88 |
// See if this storage file is locked, if so we wait upto 5 seconds for the lock owning process to |
| 89 |
// complete it's work. If the lock is not released within that time frame, it's cleaned up. |
| 90 |
// This should give us a fair amount of 'Cache Stampeding' protection |
| 91 |
if ($this->isLocked($storageFile)) { |
| 92 |
$this->waitForLock($storageFile); |
| 93 |
} |
| 94 |
if (file_exists($storageFile) && is_readable($storageFile)) { |
| 95 |
$now = time(); |
| 96 |
if (! $expiration || (($mtime = @filemtime($storageFile)) !== false && ($now - $mtime) < $expiration)) { |
| 97 |
if (($data = @file_get_contents($storageFile)) !== false) { |
| 98 |
$data = unserialize($data); |
| 99 |
return $data; |
| 100 |
} |
| 101 |
} |
| 102 |
} |
| 103 |
return false; |
| 104 |
} |
| 105 |
|
| 106 |
public function set($key, $value) { |
| 107 |
$storageDir = $this->getCacheDir(md5($key)); |
| 108 |
$storageFile = $this->getCacheFile(md5($key)); |
| 109 |
if ($this->isLocked($storageFile)) { |
| 110 |
// some other process is writing to this file too, wait until it's done to prevent hickups |
| 111 |
$this->waitForLock($storageFile); |
| 112 |
} |
| 113 |
if (! is_dir($storageDir)) { |
| 114 |
if (! @mkdir($storageDir, 0755, true)) { |
| 115 |
throw new apiCacheException("Could not create storage directory: $storageDir"); |
| 116 |
} |
| 117 |
} |
| 118 |
// we serialize the whole request object, since we don't only want the |
| 119 |
// responseContent but also the postBody used, headers, size, etc |
| 120 |
$data = serialize($value); |
| 121 |
$this->createLock($storageFile); |
| 122 |
if (! @file_put_contents($storageFile, $data)) { |
| 123 |
$this->removeLock($storageFile); |
| 124 |
throw new apiCacheException("Could not store data in the file"); |
| 125 |
} |
| 126 |
$this->removeLock($storageFile); |
| 127 |
} |
| 128 |
|
| 129 |
public function delete($key) { |
| 130 |
$file = $this->getCacheFile(md5($key)); |
| 131 |
if (! @unlink($file)) { |
| 132 |
throw new apiCacheException("Cache file could not be deleted"); |
| 133 |
} |
| 134 |
} |
| 135 |
} |
| 136 |
|
